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Abstract:

A process for optimizing status notifications in the navigation satellite
system includes the following steps: the determination of information
concerning a communication network of the navigation satellite system;
and the transmission of the determined information as a status
notification in at least one navigation message.

Claims:

1. A process for optimizing status notifications in a navigation satellite
system, said process comprising:determining information concerning a
communication network of the navigation satellite system; andtransmitting
the determined information as a status notification in at least one
navigation message.

2. The process according to claim 1, wherein the step of determining
information concerning a communication network of the navigation
satellite system comprises:determining topology of a communication
network of the navigation satellite system; anddetermining expected
continuities of communication elements of the communication network.

3. The process according to claim 1, wherein the transmission of the
determined information concerning a communication network of the
navigation satellite system takes place in the form of a navigation
message which repeats more slowly than in normal navigation messages
repeat.

4. The process according to claim 1, further comprising by transmitting a
failure of one or more communication elements in at least one alert
message.

5. The process according to claim 4, wherein said at least one alert
message contains an identification of the failed communication element.

6. A navigation satellite system comprising a space segment that includes
satellites emitting satellite signals which contain navigation messages
for the receipt and analysis by user systems for position indication and
navigation, and a ground segment that includes a plurality of observation
and command stations which monitor the satellites; wherein at least one
of the observation and command stations is configured to implement a
process for optimizing status notifications in the navigation satellite
system, including determining information concerning a communication
network of the navigation satellite system; and transmitting the
determined information as a status notification in at least one
navigation message.

7. A process for processing a status notification transmitted with a
navigation message in a navigation satellite system, said process
comprising:receiving a navigation message with a status notification
which was generated and transmitted by a process that includes
determining information concerning a communication network of the
navigation satellite system, and transmitting the determined information
as a status notification in at least one navigation message;determining
the information concerning the communication network of the navigation
satellite system contained in said status notification; andcomputing
expected continuity of the availability of observation data in the
navigation satellite system based on the determined information
concerning the communication network of the navigation satellite system.

Description:

BACKGROUND AND SUMMARY OF THE INVENTION

[0001]This application claims the priority of German patent document 10
2008 025 063.5-55, filed May 26, 2008, the disclosure of which is
expressly incorporated by reference herein.

[0002]The invention relates to a process for optimizing status
notifications in a navigation satellite system.

[0003]Global Navigation Satellite Systems (GNSS), also referred to herein
as Navigation Satellite Systems, are used for position indication and
navigation on the ground and in the air. GNSS Systems, such as the
European Navigation Satellite System (in the following, also called the
Galileo System or simply Galileo), which is currently being constructed,
include a satellite system (space segment) comprising a plurality of
satellites, an earth-fixed receiving device system (ground segment),
which is connected with a central computing station and comprises several
ground stations as well as Galileo sensor stations. User systems evaluate
and utilize the satellite signals transmitted from the satellites by
wireless communication, particularly for the navigation. The ground
stations also transmit status notifications, for example, concerning the
technical condition of all satellites in the space segment and the
integrity of the system, which notifications can be received and
evaluated by the user systems.

[0004]Because of the topology of the communication network in navigation
satellite systems like the Galileo, as a rule, several ground stations
may fail simultaneously because communication elements are used jointly
by several ground stations. Unless there is a total failure of
communication as a result of, for example, a failure of communication
elements, the continuity of the communication in the navigation satellite
system may, however, deteriorate. In particular, the transmission of
status notifications may deteriorate, which is especially disadvantageous
for the safety-critical service (Safety of Life (SoL) service) provided
in the case of the Galileo.

[0005]It is therefore an object of the present invention to provide a
process for optimizing status notifications in the case of a navigation
satellite system.

[0006]This and other objects and advantages are achieved by the process
and system according to the invention, in which information concerning a
communication network of a navigation satellite system, such as the
topology of the communication network or the expected continuity of its
communication elements, is transmitted to user systems for further
processing. A user system can thereby compute the expected continuity of
the availability of observation data of the navigation satellite system.
This process permits optimization of status notifications in the
navigation satellite system because a user system can calculate a
possibly impaired continuity of the communication, particularly of status
notifications, by processing of the received information concerning the
communication network, a precision with which distance measurements can
be carried out.

[0007]According to an embodiment of the invention, a process is provided
for optimizing status notifications in the case of a navigation satellite
system, having the following steps: [0008]Determination of information
concerning a communication network of the navigation satellite system;
and [0009]transmission of the determined information as a status
notification by means of one or more navigation messages. As a result of
the transmission of information concerning the communication network, a
user system can determine the continuity to be expected, and based
thereon emit, for example, a warning message concerning a reduction of
distance measurements based on navigation messages that could possibly be
expected.

[0010]According to the invention, the step of determining information
concerning a communication network of the navigation satellite system can
comprise the following steps: [0011]Determining the topology of a
communication network of the navigation satellite system; and
[0012]determining the expected continuities of communication elements of
the communication network. The latter can enable a user system to develop
a precise estimate of a continuity of navigation messages to be expected,
because knowledge of the topology and of the expected, continuities of
the communication elements permits an overall estimate of the continuity
in the navigation satellite system.

[0013]According to a further embodiment of the invention, the transmission
of the determined information concerning a communication network of the
navigation satellite system can take place in the form of a navigation
message that is repeated more slowly than normal navigation messages. As
a result, the flow of communication in the navigation satellite system is
affected only a little by the transmission of the information on the
communication network.

[0014]According to another embodiment of the invention, the step of
transmitting the failure of one or more communication elements is
performed by one or more alert messages, which rapidly inform the user
systems concerning the failure, so that the latter can newly compute the
continuity and, as required, adapt to the newly computed continuity.
Furthermore, as a result, faults which the availability of measuring data
of several ground stations of the navigation satellite system can now be
disseminated clearly more effectively in alert messages.

[0015]In particular, according to an embodiment of the invention, an alert
message may contain an identification of the failed communication
element, so that the user systems will be able to compute as precisely as
possible the continuity change because of the failure. This eliminates
the necessity of marking every individual observation station as
unavailable in a single alert message, because the isochronous failure of
several observation stations is almost always caused by the failure of
elements of the communication.

[0016]The invention also relates to a navigation satellite system, which
comprises a space segment having satellites which emit satellite signals
containing navigation messages for receipt and analysis by user systems,
for the position determination and navigation, and a ground segment
having several observation and command stations monitoring the
satellites. One or more of the observation and command stations are
constructed for executing a process according to the invention and
described above, in order to optimize the status notifications in the
navigation satellite system. In such a navigation satellite system, on
the one hand, a user system can clearly better model the efficiency of
the observation system for its purposes, and, on the other hand,
different user demands can better be satisfied by means of a single data
stream.

[0017]Furthermore, the invention provides a method for processing a status
notification transmitted by a navigation message in a navigation
satellite system, having the following steps: [0018]Receiving of a
navigation message with the status notification which was generated and
transmitted by means of a process according to the invention, as
described above; [0019]determining the information concerning the
communication network of the navigation satellite system contained in the
status notification of the received navigation message, and
[0020]computing the expected continuity of availability of observation
data in the navigation satellite system on the basis of the determined
information concerning the communication network of the navigation
satellite system.

[0021]Finally, the invention provides a receiver for signals of a
navigation satellite system which contain navigation messages. The
receiver is constructed to implement a process for processing a status
notification transmitted by means of a navigation message in a navigation
satellite system according to the invention, as explained above. For
example, the process can be implemented in the operating software of a
receiver for navigation messages, such as a navigation device. As a
result, the functionality of the receiver can be expanded, in that it
can, more precisely than previously, inform a user concerning a possible
problem in the continuity, as well as the continuity to be expected.

[0022]Other objects, advantages and novel features of the present
invention will become apparent from the following detailed description of
the invention when considered in conjunction with the accompanying
drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a view of a navigation satellite system with an embodiment
of a system for optimizing status notifications in a navigation satellite
system according to the invention; and

[0024]FIG. 2 is a flow chart of an embodiment of a process for optimizing
status notifications in the case of a navigation satellite system
according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0025]The terms and assigned reference symbols used in the attached list
of reference symbols will be used in the specification, in the claims, in
the abstract and in the drawings. The same and/or functionally identical
elements may be provided with the same reference symbols.

[0026]FIG. 1 illustrates a navigation satellite system 10 having a space
segment 2 and a ground segment 20. The space segment 12 comprises several
satellites 14, each of which orbits around the ground segment 20. Each
satellite emits satellite signals 16, which can be received by user
systems 18, such as mobile navigation devices, as well as by observation
and command stations 22 of the ground segment 20. The satellite signals
16 contain navigation messages of the navigation satellite system 10,
which navigation messages contain orbital parameters for the description
of the orbit.

[0027]The observation and command stations 22 which, in the case of the
Galileo System, are designed as separate units, are provided particularly
for the monitoring and controlling of the satellites 14. For this
purpose, they transmit received navigation signals 16 by way of a
communication network to a control center 24 (central processing point of
the ground segment 20) which analyzes the received navigation signals 16.
That is, it examines the data of a satellite 14 transmitted with each
navigation signal 16, particularly the orbit and point in time of the
generating of the signal as well as the signal structure and integrity of
the received signals. The observation and command stations 22 further
generate navigation messages 28, which may contain the previously
mentioned status notifications (for example, concerning the technical
condition of all satellites of the space segment and the integrity), and
continuously send them to the satellites 14 for the continuous further
distribution to the use systems 18. From the navigation messages 28
received by means of the satellite signals 16, a user system 18 can
obtain information concerning the integrity, and thus the reliability, of
the received navigation-relevant data.

[0028]Particularly for critical services, like the initially mentioned SoL
Service in the case of Galileo, a continuous data stream in the
communication network of the ground segment 20 is significant because it
ensures that the user systems 18 utilizing the SoL Service are notified
as fast as possible of problems in the navigation system 10. An example
of a SoL Service is satellite-supported navigation during an approach of
an airplane.

[0029]The topology of the communication network of the Galileo is
therefore basically constructed such that, even in the event of a failure
of individual communication elements, such as one or more observation
stations 22, a continuous data stream is maintained. However, the system
continuity may be impaired by the failure, and may mainly deteriorate,
for example, by an increase of the delay time before an important message
arrives at a user system. As a result of a failure, the propagation time
of messages which are transmitted from the ground segment 20 by way of
the space segment 12 to the user systems 18 may increase, or the
continuity of the messages emitted from the ground segment 20 may
fluctuate.

[0030]The navigation messages 28 emitted by the ground segment 20
therefore contain information concerning the communication network of the
navigation satellite system 10, such as the topology of the communication
network and the expected continuities of communication elements of the
communication network. In an observation and command station 22, this
information may also be embedded in a navigation message 28, which, in
comparison to normal navigation messages, is transmitted to the user
systems 18 by way of the satellite signals 16 at a slower rate of
repetition. By means of this information, a correspondingly constructed
user system 18 can compute the expected continuity, particularly of the
availability of observation data at the control center 24.

[0031]Should a communication element (for example, a satellite 14 or an
observation and command station 22) have failed, an alert message can
also be sent out with a navigation message 28 from a ground and command
station 22. This alert message may contain information concerning the
failed element, so that, based on the information concerning the
communication network (particularly the topology and the expected
continuities of the individual communication elements) and the
information concerning the failed element, a user system 18 can compute
the continuity with which observations are available at the control
center 24. By means of the information available at the control center
24, a user system 18 can then further determine the precision with which
distance measuring signals can be observed. The higher the demand of the
user system 18 for continuity, the poorer the assumed precision of the
observation, since several observations are required for providing the
continuity.

[0032]For embedding the topology information and expected continuity
information in a navigation message 28, an observation and command
station 22 has corresponding processor devices 26, which are configured
to implement the process illustrated by the flow chart in FIG. 2, for
example, in that they implement corresponding algorithms.

[0033]According to the course of the process depicted in FIG. 2,
information concerning a communication network of the navigation
satellite system is first determined in Step S10, which is divided into
two substeps: In Step S102, the topology of a communication network of
the navigation satellite system is determined first. (The topology can be
stored, for example, in the control center 24 and can be retrieved by an
observation and command station 22 by way of the communication network.)
In the subsequent Step S104, the expected continuities of communication
elements of the communication network will then be determined. Data
concerning the expected continuities of the communication elements can be
stored, for example, in a data bank of the control center 24 and can be
retrievable by the observation and command stations 22.

[0034]For carrying out Step S10, the processor devices 26 of the
observation and command station 22 can, for example, first initiate the
querying of the topology from the control center and intermediately store
data concerning the topology received from the control center 24, in
order to subsequently identify the communication elements indicated in
the data concerning the topology and retrieve their expected continuities
from the data bank of the control center 24. From the date thus obtained,
the processor devices 26 can subsequently generate a navigation message
28 which is transmitted to the satellites 14 of the space segment 12 in a
slow sequence. The information concerning the communication network
contained in the transmitted navigation message 28 represents status
notifications concerning the navigation satellite system in a broader
sense, and concerning the communication network of the navigation
satellite system in a narrower sense. The control center 24 can further
automatically signal changes of the topology and of the expected
continuities to the individual observation and command stations 22 of the
ground segment 20, so that these can automatically correspondingly adapt
the slowly repeating navigation message.

[0035]As a result of the invention, a user system of a navigation
satellite system can better model the efficiency of an observation system
of a navigation satellite system for its purposes. Furthermore, it
becomes possible to meet users' various demands by means of a single data
stream because the user systems will be able to carry out their own
computations concerning the continuity to be expected by means of the
transmitted information relative to the communication network.
Furthermore, faults relating to the availability of measuring data of
several ground stations, particularly observation and command stations,
can be disseminated significantly more effectively in alert messages.
Finally, the necessity of marking each individual observation and command
station as unavailable in a single alert message can be eliminated,
because the isochronous failure of several observation stations is almost
always caused by the failure of elements of the communication in the
navigation satellite system.

[0036]The foregoing disclosure has been set forth merely to illustrate the
invention and is not intended to be limiting. Since modifications of the
disclosed embodiments incorporating the spirit and substance of the
invention may occur to persons skilled in the art, the invention should
be construed to include everything within the scope of the appended
claims and equivalents thereof.